Mention was made that you may have to file an estate tax return Form 706 (PDF), United States Estate (and Generation Skipping Transfer) Tax Return. Please refer to the Form 706 Instructions to determine if a Form 706 is required to be filed.
The personal representative (executor) is responsible for filing tax returns for a person who has died, and for the decedent's estate. The personal representative may be required to file the final income tax return and any returns not filed for preceding years.
The filing requirements that apply to individuals will determine if a final income tax return is required for the decedent. Refer to Publication 17, Your Federal Income Tax, for additional information. The final return should show only the items of income the decedent actually received, that were credited to his account, or that were made available to him without restriction before death. Generally, expenses the decedent paid before death should be deducted on the final return.
You also may have to file an income tax return for the estate, whether or not there is a requirement for the estate tax return. The estate usually will have an income tax filing requirement if there is more than $600 of income in the year starting on the date of death. Please refer to the Form 1041 Instructions to determine if a Form 1041 (PDF), U.S. Income Tax Return for Estates and Trusts, is required to be filed.
Form 56 (Rev. December 2007 ,Notice Concerning Fiduciary Relationship, is used to notify the Internal Revenue Service and state taxing authorities of either the initiation or termination of your fiduciary relationship.
See the publication at http://www.irs.gov/publications/p559/ix01.html for more details.
I hope this helps.